STORY ARCHIVE

Snowball Earth

TRANSCRIPT

Narration: Today, when you think of ice and glaciers you think of the poles – of the high latitudes of the world.

Paul Willis: Perhaps the last place you’d expect to find a glacier is here in the Flinders Ranges of South Australia. But these rocks tell the story of a very different planet from the one we know today.

Narration: Meet geologist Galen Halverson. We’re in Brachina Gorge, walking over rocks that are more than 630 million years ago. It was a time of the Mother of all Climate Changes.

Paul: These rocks have got the classic signatures of glaciers. Most of it is purple sandstone but occasionally you get large stones like this which couldn’t possibly have washed in under the action of water. This stone’s been picked up by a glacier. It’s moved out to sea and become icebergs and as those icebergs melt, the stones drop onto the sea floor. It’s called a drop-stone. So while the stones here definitely tell me that this was a glacial environment just above me where Galen is tell a completely different story.

Dr Galen Halverson: So this rock type here is called a “Cap Carbonate”. This type of rock usually only forms in tropical environments like the Bahamas. What’s extraordinary is the very same rock type occurs all over the world. Everywhere these glacial deposits occur. So what it indicates is a switch from Antarctic glacial conditions to tropical conditions in a geological bat of the eye.

Narration: Galen has seen these glacial rocks capped with carbonate all around the world at this time. So what’s the story? Galen and his colleagues say we are looking at the signature of a time when the whole world was frozen under ice. And they call this theory “Snowball Earth”.

It’s hard to imagine today that this place, and every other part of the planet, was once under a sheet of ice kilometres thick. From the highest mountain to the deepest ocean, a continuous white planet that reflected most of the sun’s heat and light back into space. But how do you trigger a “Snowball earth”? The secret is in the position of the continents.

Paul: Now, we know that the continents have been sliding around the face of the earth for hundreds of millions of years. But continents reflect more sunlight than sea water. So if the continents are arranged around the equator where the most sunlight is, the world will be cooler and it’ll be easier to slip into a snowball earth.

Narration: So one focus of the Snowball Earth researchers is trying to figure out exactly where the continents were. And here’s a clue.

Paul: These rocks are a rare and very important kind of rock called a “Tidal Rhythmite”. Each of the little layers you can see here was laid down by an individual tide some 630 million years ago. So if we study them closely we can actually work out the movements of the moon and the earth all that time ago. It turns out that there were 30 days to the lunar month, 400 days to a year and each of those days was only 22 hours long. And this hole here, that tells us a completely different story.

Narration: These holes were drilled by geologists looking for evidence of what the earth’s magnetic field was like 630 million years ago. Tiny particles within the sediments have lined up with the earth’s magnetic field when the rocks were laid down. As Alan Collins explains, reading these particles can tell us the geographical position of the continents at that time.

Dr Alan Collins: So what these holes have been taken to measure, is to try and work out, using very sensitive magnetometers, what angle that makes with respect to these bedding surfaces, which was horizontal on the earth at the time. Turns out when you look at these, the magnetic vector preserved in these rocks, is pretty much horizontal in respect to this bedding. So we know we were roughly at the equator, plus a minus ten degrees from the equator, at the time these rocks were laid down.

Narration: When Alan’s not teaching students the elements of geology on the field, he works on Continental Drift and Snowball Earth.

Dr Collins: I’m not completely un-skeptical about the Snowball Earth, there are things that are fairly difficult to explain in the Snowball Earth theory. It does however, explain why we’re getting all these low latitude glaciations at sea level around the earth. To me it seems the most logical way of explaining the observations.

Narration: Other researchers are much more sceptical. Victor Gostin works just down the corridor from Galen and Alan at the University of Adelaide.

Dr Victor Gostin: What I see is certainly major ice ages, major glaciations, evidence of advance and retreat of the ice, but I don’t really see that it was all totally frozen at any time.

Narration: The critics of Snowball Earth have forced its supporters back into the laboratory to back up their claims. Accurate, reliable dating of the rocks concerned right around the world is part of the research to show if these events were truly global and contemporaneous. Another objection concerns the other end of a Snowball event.

Dr Gostin: And if you did have it totally frozen, it’d be almost impossible to get it out of the frozen state. So, there are two sorts of arguments which are being published, and we’re saying, well, okay, at least modelling the idea of a totally frozen earth given the distribution of continents and so forth is very difficult but it shows us A) it’s hard to get into a totally frozen earth, and B) if you’re there, it’s hard to get out of it.

Narration: Galen, thinks he has the answer. Even in the depths of the deepest Snowball, volcanos would still be active, pumping ever-increasing quantities of greenhouse gases into the atmosphere.

Dr Galen Halverson: Over millions of years enough would accumulate such that the greenhouse effect of the CO2 would overcome the ice albedo effect and start melting the ice. Once the ice starts to melt it would melt down extremely quickly, in the order of a few thousand years.

Narration: The runaway greenhouse effect would flip the world from a Snowball to a tropical furnace in a geological instant. That’s why Galen sees tropical cap carbonates sitting on top of glacial deposits right around the world. And there’s a post script to this story that has direct implications for you and me.

Paul: These rocks were laid down at the end of that last great glaciation. And the younger rocks on top of the hill behind me, they contain some of the oldest multi cellular fossils in the world. Now, no-one’s quite sure how, but the suspicion is that, if it wasn’t for Snowball Earth, life wouldn’t have got a big kick in the guts that ended up as the diversity of life that we see around us today.

Narration: So, could the earth tip once again into a giant snowball?

Dr Halverson: I’d say a snowball’s chance of having another snowball. Once life inhabited the continents and, and the oceans, it essentially established really strong feedback and mechanisms that prevent the climate from getting too terribly cold or too terribly hot. So I doubt we’ll ever see another snowball event.

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YOUR COMMENTS

Dear Dr. , I propose that the â€śsnow ball Earthâ€ť was brought to a close by the dust from a huge meteorite (the largest known on Earth) impacting Australia settling onto the ice and melting it by a bare soil warming affect and thus initiating the Cambrian. The dust fertilizing the ocean probably contributed considerably to the explosion of life then. That initiation was probably considerably assisted by the subsequent release of methane gas from methane ice under the ocean floor and by dust from volcanic eruptions from the Bahamas Islands, which are located at the antipode (opposite side of a sphere) of the above impact. The close correlation of volcanoes on Mars with meteorite impacts at their antipodes gives supporting evidence for such a phenomenon. for Mars. Sincerely, Charles Weber